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Date: Thu, 11 Nov 2004 10:33:37 -0500
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From: "Gary Casey" <glcasey@adelphia.net>
Subject: Re: Halon fire extinguishers
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<<I (think that I) had read that the Navy does not want av gas on board
ship because it is more of a fire problem compared to jet fuel, and I
believe that jet fuel and diesel are interchangeable.  Are our turbine
brothers carrying around that much greater risk?>>

There are really 2 main factors in the "hazard" associated with oil and
gasoline.  One is the ignition temperature, where gasoline has a higher
ignition temperature than jet fuel, diesel fuel and lube oil, which are all
about the same.  However, ignition temperature is a complex phenomena and is
a function of time, pressure, temperature and mixture.  The high ignition
temperature of gasoline is related to the octane number and that's why
gasoline works to resist detonation in a spark-ignition homogenous-charge
engine. The other factor is the so-called "flash point" and that is roughly
the temperature at which enough of the liquid evaporates from a pool so that
it can be ignited by an open flame.  Gasoline has a very low flash point
and, depending on the vapor pressure,  is probably in the -20 to +20F range.
The flash point of the other oils is more like 100 to 300F, Jet A being the
lowest and lube oil being the highest.  The result of all this is that you
can spray gasoline on the red-hot exhaust pipe of a running engine and it
probably won't ignite.  Do the same with engine oil and it will certainly
start on fire.  However, you can crash an airplane, dumping oil all over it
with something sparking and it won't burn.  Have spilled fuel anywhere
around and it will burn.  I remember reading that most race car fires are
started by oil, not the fuel and I think it would be very wise to make sure
that none of the oil lines in the engine compartment could leak in a way
that oil would impinge on the exhaust system.  Which is more dangerous,
gasoline or jet fuel?  It depends.

Gary Casey